1. Field of Invention
This invention relates generally to gears used in pumps for liquids, and more particularly, to gears of positive displacement gear pumps.
2. Description of Related Art
Typical spur gear pumps are not very efficient when handling low viscosity liquids. As viscosity decreases, internal slip within the pump increases. Thus in common spur gear pumps, low viscosity liquids slip or flow backwards around the gears through clearance areas between the gears, or gear wheels, and interior walls of their housing. This slippage reduces output flow of the liquids. U.S. Pat. No. 5,297,945 to Loubier, et al. discloses a pump with oval or elliptical gears for viscous liquids such as syrups, etc. The pump is not very efficient for lower viscosity liquids because discharge pressure causes much of the fluid to flow backwards past the pumping gears. In addition, liquid displacement is limited to the size or length of the gears.
Spur gear and helical gear pumps displace a volume of liquid per revolution that is equivalent to the volume of all the intermeshing teeth of the gears in a full rotation of 360°. The volume has practical limits in relation to the size and number of teeth that given gear diameter can accommodate. U.S. Pat. No. 6,048,186 to Kitano discloses elliptic gear wheels with larger teeth at the ends of the major axis. However, this pump is also not very efficient for lower viscosity liquids. Further, the pump volume is limited to the length along the major diameter axis.
The inventor has realized a benefit to efficiently seal and displace low viscosity fluids. Some examples of relatively low viscosity liquids include water, ethanol, milk, kerosene, diesel fuel, etc.
All references cited herein are incorporated herein by reference in their entireties.